Gabriel shocks have been around since I was a teenager, perhaps longer, I think the company was bought out yonks ago, not the best around.
Monroe are what GM use as a replacement strut / shock, they have been around just as long.
Just remember that gas shocks will make every pebble feel like a pot hole, if you can still get em stick with heavy duty oil only shocks, gas is usually preferred when carrying heavy loads or your springs are weak.
In the early 70's when the 350 monaro was new they ran the best shocks made, which fited many other model holdens, good chance there is a company that still makes a similar type, worth a look anyway.
Pedders are $exe but there is more choice available, the Heavy Duty sensa-trak versions seem to do OK.
EG; the HJ-75 landcruiser was like rigid suspension when empty but with a full tank 90 lit and 500 kgs in the back the gas shocks were great.